1. Field of the Invention
This invention relates to the grounding of electrical conductors and more particularly to the provision of a medium in which a ground electrode ma be embedded for advantageous results.
2. Description of the Prior Art
Ground electrodes have been used for many purposes well known in the art. One type has included a metal conductor, post or pipe arranged in contact with carbonaceous material such as coke or charcoal to enlarge the effective area of contact between the metal conductor and the earth. These have generally depended on maintaining the presence of moisture and have included containers for holding th material in contact with the conductor. They have been subject to the problems of drying out, corrosion, instability and fluctuation in conductivity. Examples of U.S. patents directed to this type of ground are Jones, 873,375, Turner, U.S. Pat. No. 895,916, Pardee, U.S. Pat. No. 1,013,305, Banks, U.S. Pat. No. 1,111,783, Brach, U.S. Pat. No. 1,138,186, Vogel, U.S. Pat. No. 1,288,303, Preston, U.S. Pat. No. 1,856,506, Mudd, U.S. Pat. No. 2,552,208 and Heise, U.S. Pat. No. 2,553,654.
Another type of ground electrode is employed at or just beneath the surface of the earth in order to reduce the step potential differences across the earth or a surface for walking, as for example at an electrical utility substation. Thus, during an electrical fault, high magnitude electrical potential differences may be present which would constitute a hazard to an individual walking in the area. In order to meet this problem, a common practice has been to bury bare copper grounding wires forming a mesh arrangement in the affected area.
Various arrangements and compositions of carbonaceous materials in a matrix system, including concrete, for use on various surfaces, walkways, floors, roadways and the like are described in the U.S. patents to Minsk, U.S. Pat. No. 3,573,427, Freeman et al., U.S. Pat. No. 3,962,142, Wiley, U.S. Pat. No. 4,806,272 and in Japanese patents Nos. JE0044233 of November 1978 and JA0126282 of October 1981.
The above mentioned U.S. patent to Freeman et al. discloses a settable composition including a cementitious material and an aggregate which includes carbonaceous material of at least two types, one type being relatively large carbonaceous particles and the other type being relatively small carbonaceous particles. Examples of the relatively large carbonaceous particles are calcined oil coke. An example of the relatively small particles is acetylene black.
The U.S. patnet to Nigol et al., 3,941,918 discloses a cement for mechanically and electrically joining metal hardware to an insulator shell, the cement including portland cement admixed with graphite fibers and high structure carbon black.